The present invention relates generally to performance measuring systems for use with bicycles and, more particularly, to a chain ring based power measuring apparatus that measures the amount of work done by a cyclist to rotate a wheel of a bicycle.
Power is generally defined as the product of torque and angular velocity or the product of force and velocity. In this regard, power cannot be determined directly, but can be calculated from torque and velocity information acquired as the cyclist propels the bicycle. As power corresponds to work done, cyclists are increasingly outfitting their bicycles with power measuring systems that provide speed and power feedback, such as instantaneous speed, instantaneous power, average speed, average power, and other metrics to assess the intensity of a ride.
Conventional power measuring systems, commonly referred to as “power meters”, typically measure torque and angular velocity in either the driving components of the bicycle, such as the pedals and crank arms, or in the driven components of the bicycle, such as the chain rings, chain, and rear wheel. U.S. Pat. No. 6,418,797, the disclosure of which is incorporated herein, describes a rear wheel hub assembly that has torque and angular velocity sensing components as well as electronics that use torque and angular velocity information to calculate power and other performance metrics, the values of which may be displayed on a handlebar mounted display.
One of the drawbacks of conventional power measuring systems, especially those that measure torque and angular velocity in a driven component, has been the difficulty in incorporating such a system into a bicycle. Typically, it is necessary to employ a mechanic having the appropriate tools and training necessary to disassemble and remove the driven components of the rear wheel, install the power measuring system and then reassemble the driven components. Recreational cyclists, however, generally lack the tools and skill set to properly make such a modification.
Additionally, many power measuring systems have components that replace one or more of the original components of the bicycle, such as the crank set or the rear hub. For a competitive cyclist or enthusiast, the benefits associated with the information provided by a power meter are often found to outweigh the costs of discarding an original component despite the original component being in working condition. A recreational cyclist, on the other hand, may object to the cost associated with replacing the crank set or the rear hub.